The Centers for Disease Control and Prevention describe how to tell if you have asthma:

How Can You Tell if You Have Asthma?
It can be hard to tell if someone has asthma, especially in children under age 5. Having a doctor check how well your lungs work and check for allergies can help you find out if you have asthma.
During a checkup, the doctor will ask if you cough a lot, especially at night, and whether your breathing problems are worse after physical activity or at certain times of year. The doctor will also ask about chest tightness, wheezing, and colds lasting more than 10 days. They will ask whether anyone in your family has or has had asthma, allergies, or other breathing problems, and they will ask questions about your home. The doctor will also ask if you have missed school or work and about any trouble you may have doing certain things.
The doctor will also do a breathing test, called spirometry, to find out how well your lungs are working. The doctor will use a computer with a mouthpiece to test how much air you can breathe out after taking a very deep breath. The spirometer can measure airflow before and after you use asthma medicine.
What Is an Asthma Attack?
An asthma attack may include coughing, chest tightness, wheezing, and trouble breathing. The attack happens in your body’s airways, which are the paths that carry air to your lungs. As the air moves through your lungs, the airways become smaller, like the branches of a tree are smaller than the tree trunk. During an asthma attack, the sides of the airways in your lungs swell and the airways shrink. Less air gets in and out of your lungs, and mucous that your body makes clogs up the airways even more.
You can control your asthma by knowing the warning signs of an asthma attack, staying away from things that cause an attack, and following your doctor’s advice. When you control your asthma:
• you won’t have symptoms such as wheezing or coughing,
• you’ll sleep better,
• you won’t miss work or school,
• you can take part in all physical activities, and
• you won’t have to go to the hospital.
What Causes an Asthma Attack?
An asthma attack can happen when you are exposed to “asthma triggers”. Your triggers can be very different from those of someone else with asthma. Know your triggers and learn how to avoid them. Watch out for an attack when you can’t avoid the triggers. Some of the most common triggers are tobacco smoke, dust mites, outdoor air pollution, cockroach allergen, pets, mold, and smoke from burning wood or grass…. http://www.cdc.gov/asthma/faqs.htm

Urban trees can affect the quality of life and health.

The Nature Conservancy published How Urban Trees Can Save Lives:

The Planting Healthy Air report documents which cities stand to benefit most from tree plantings, in terms of both heat and PM reduction, and how much investment would be required to achieve meaningful benefits.
The analysis found that investing just US$4 per resident in each of these cities in tree planting efforts could improve the health of millions of people, and that trees are as cost-effective as many other common solutions.
Most of the cooling and filtering effects created by trees are fairly localized, so densely populated cities—as well as those with higher overall pollution levels—tend to see the highest overall return on investment (ROI) from tree plantings…. https://global.nature.org/content/healthyair

Exeter University reported that asthma attacks were reduced in tree-lined urban areas.

People living in polluted urban areas are far less likely to be admitted to hospital with asthma when there are lots of trees in their neighbourhood, a study by the University of Exeter’s medical school has found.
The study into the impact of urban greenery on asthma suggests that respiratory health can be improved by the expansion of tree cover in very polluted urban neighbourhoods.
The study, published in the journal Environment International, looked at more than 650,000 serious asthma attacks over a 15 year period. Emergency hospitalisations were compared across 26,000 urban neighbourhoods in England.
In the most polluted urban areas, trees had a particularly strong association with fewer emergency asthma cases. In relatively unpolluted urban neighbourhoods trees did not have the same impact.
In a typical urban area with a high level of background air pollution — for example, around 15 micrograms of fine particulate matter (PM2.5) per cubic metre, or a nitrogen dioxide concentration around 33 micrograms per cubic metre — an extra 300 trees per square kilometre was associated with around 50 fewer emergency asthma cases per 100,000 residents over the 15 year study period.
The findings could have important implications for planning and public health policy, and suggest that tree planting could play a role in reducing the effects of air pollution from cars.
Over 5.4 million people receive treatment for asthma in the UK with an annual cost to the NHS of around £1 billion. 18 per cent of adults report asthma in the previous 12 months, and a quarter of 13-14 year olds report symptoms. Asthma causes over a thousand deaths a year.
The study led by Dr Ian Alcock, research fellow at the University of Exeter’s Medical School, found that trees and green space were both related to a decrease in people admitted to hospital with asthma…. https://www.sciencedaily.com/releases/2017/11/171117103814.htm

Asthma attacks reduced in tree-lined urban neighbourhoods
People living in polluted urban areas are far less likely to be admitted to hospital with asthma when there are lots of trees in their neighbourhood, a study by the University of Exeter’s medical school has found.
The study into the impact of urban greenery on asthma suggests that respiratory health can be improved by the expansion of tree cover in very polluted urban neighbourhoods.
The study, published in the journal Environment International, looked at more than 650,000 serious asthma attacks over a 15 year period. Emergency hospitalisations were compared across 26,000 urban neighbourhoods in England.
In the most polluted urban areas, trees had a particularly strong association with fewer emergency asthma cases. In relatively unpolluted urban neighbourhoods trees did not have the same impact.
In a typical urban area with a high level of background air pollution – for example, around 15 micrograms of fine particulate matter (PM2.5) per cubic metre, or a nitrogen dioxide concentration around 33 micrograms per cubic metre – an extra 300 trees per square kilometre was associated with around 50 fewer emergency asthma cases per 100,000 residents over the 15 year study period.
The findings could have important implications for planning and public health policy, and suggest that tree planting could play a role in reducing the effects of air pollution from cars.
Over 5.4 million people receive treatment for asthma in the UK with an annual cost to the NHS of around £1 billion. 18 per cent of adults report asthma in the previous 12 months, and a quarter of 13-14 year olds report symptoms. Asthma causes over a thousand deaths a year.
The study led by Dr Ian Alcock, research fellow at the University of Exeter’s Medical School, found that trees and green space were both related to a decrease in people admitted to hospital with asthma.
Dr Alcock said:
“We wanted to clarify how urban vegetation may be related to respiratory health. We know that trees remove the air pollutants which can bring on asthma attacks, but in some situations they can also cause localised build-ups of particulates by preventing their dispersion by wind. And vegetation can also produce allergenic pollen which exacerbates asthma.
We found that on balance, urban vegetation appears to do significantly more good than harm. However, effects were not equal everywhere. Greenspace and gardens were associated with reductions in asthma hospitalisation at lower pollutant levels, but not in the most polluted urban areas. With trees it was the other way round. It may be that grass pollens become more allergenic when combined with air pollutants so that the benefits of greenspace diminish as pollution increases. In contrast, trees can effectively remove pollutants from the air, and this may explain why they appear to be most beneficial where concentrations are high.”
Co-author Dr Rachel McInnes, Senior Climate Impacts Scientist at the Met Office, added: “This finding that the effects of different types of vegetation – green space and gardens, and tree cover – differ at both very high and very low air pollution levels is particularly relevant for public health and urban planning policies. We also know that the interaction between pollen and air pollution, and the effect on health and asthma is highly complex and this study confirms that more research is required in this area. Large collaborative research projects, like this from the NIHR Health Protection Research Unit in Environmental Change and Health are a very effective way to carry out this type of cross-disciplinary work.”
Date: 17 November 2017 http://www.exeter.ac.uk/news/university/title_622600_en.html

Pascal Mittermaier wrote in Why Plant Trees in Cities? Because They Protect Our Most Vulnerable Residents:

So how do we make cities cooler and healthier? Urban planners and public health officials are grappling with the best way to approach this issue. But there’s one solution we can implement now: plant more trees. Trees and other vegetation naturally cool the air around them by shading surfaces and releasing water vapor. While the effects are local—most of the improvement is within 100 meters—they can still be meaningful, reducing temperatures by up to 2°C.
Trees also provide another significant public health benefit: they reduce fine particulate matter air pollution, a problem that contributes to 5 percent of all deaths worldwide each year. Our organization, The Nature Conservancy, has carried out a study of 245 cities around the world that stand to benefit from tree-planting initiatives, assessing their efficiency and return on investment. Compared to other ways to cool outdoor air temperatures and reduce fine particle matter, trees deliver similar benefits per dollar spent—and, planting trees is the only intervention that addresses both air pollution and heat…. https://newcities.org/perspectives-why-plant-trees-in-cities-because-they-protect-our-most-vulnerable-residents/

One program which all residents of urban areas can participate is the planting of urban trees and encouraging public officials to expand and protect tree canopy.